The invention relates to standards for evaluating oxide removal, methods of making the standards, and their associated methods of use.
Aeronautical, marine, and land-based turbine components, such as, but not limited to, blades, shrouds, and vanes, are exposed to high-temperature oxidizing, and often corrosive, environments during service. Surfaces of turbine components, including cracks, may form complex, chemically stable thermal oxides during use. These oxides comprise, but are not limited to, oxides of aluminum, titanium, chromium, and combinations thereof.
Turbine components are periodically overhauled in order to prolong life or enhance performance. During these overhauls, the turbine components may be subjected to various repair operations, including welding, brazing, or coating. The presence of stable oxides impairs the reparability of a superalloy. Therefore, removal of these oxides prior to repair, for example by cleaning the turbine components, is important for successful turbine overhaul.
Grit-blasting or grinding operations can effectively remove surface oxides when only superficial repairs are required and the surfaces to be cleaned are readily accessible. These cleaning operations, however, are not only labor intensive but can result in inadvertent and undesirable loss of the base alloy material, thus compromising the turbine component""s reliability and efficiency. Further, repair of hard-to-reach surfaces, including internal passages and highly concave sections, such as, but not limited to, cooling holes, cracks, and slots, generally requires a non-mechanical cleaning process that minimally degrades or consumes the base alloy. These cleaning processes have included batch thermo-chemical cleaning, such as processes that occur in a high-temperature reactive environment. These batch turbine-component cleaning processes can, in some cases, rely on fluoride ions, which are provided in a reactor to remove highly stable oxides from cooling holes, cracks, slots, and other hard-to-reach surfaces. The fluoride-ion cleaning (FIC) processes are known to remove oxides while leaving the turbine component""s base alloy essentially intact.
While processes such as FIC are useful for cleaning oxides on turbine components, the process effectiveness, especially with respect to oxide removal from cooling holes, cracks, slots, and other hard-to-reach surfaces, is difficult to quantify. Known measures of oxide removal comprise sectioning of cleaned turbine components and measuring the extent of oxide cleaning. This measure does not provide a consistent indication of overall oxide removal, since both the damage and oxidation characteristics of each turbine component will vary. Therefore, a tool that can consistently gauge the effectiveness of an oxide removal process would be desirable.
The invention sets forth an article of manufacture comprising a block of material upon which an oxide can be formed and a defect structure disposed in the block of material. The article is capable of being used to assess the effectiveness of an oxide removal process by measuring oxide removal from the block and defect structure after subjecting it to an oxide removal process.
The invention further sets forth a tool for determining oxide removal parameters of an oxide removal process. The tool comprises a block of material upon which an oxide can be formed and a defect structure disposed in the block of material. The tool is capable of being used to assess the effectiveness of an oxide removal process by measuring oxide removal from the block and defect structure after subjecting it to an oxide removal process.
Another embodiment of the invention provides a process for determining an oxide removal effectiveness. The process comprises disposing an oxidized standard in a reactor that is capable of oxide removal. The standard comprises a block of material upon which an oxide can be formed and a defect structure disposed in the block of material. The method further includes conducting an oxide cleaning and evaluating the standard for remaining oxide.
A further embodiment of the invention comprises a process for forming an oxide removal evaluation standard. The standard comprises a block of material upon which an oxide can be formed and a defect structure disposed in the block of material. The process comprises machining the slot structure in the block of material, compressing the defect structure to form at least one crack-like defect, and exposing the block of material to a thermal treatment to form an oxide on the block surfaces and within the at least one crack-like defect.
These and other aspects, advantages and salient features of the invention will become apparent from the following detailed description, which, when taken in conjunction with the annexed drawings, where like parts are designated by like reference characters throughout the drawings, disclose embodiments of the invention.